feat(usb): a USB keyboard -- a full one -- and no hang on a PC without PS/2

boards/BRINGUP.md A3 and S3, FABRIC-3 SXLI.  A HID boot keyboard is
configured (interrupt IN endpoint, SET_PROTOCOL boot) and its reports
become the same Linux-keycode events as PS/2 and virtio (usb_kbd.c): the
full layout -- F-keys, navigation block, arrows, Num Lock, keypad.  The
console treats Caps and Num Lock as toggles shown on the keyboard's
lights, and the keypad as digits or navigation.  While a USB keyboard
runs, its event ring is serviced every tick, not once a second.

Found on the way: with no i8042 (port 0x64 reads 0xFF) the kernel hung at
boot in an endless drain -- a legacy-free PC would stop there.  Detected
and skipped now; drains bounded.

QEMU, amd64 with the USB keyboard the only one: 1 2 + . on main keys and
keypad, Caps Lock, Num Lock all right; aarch64/riscv64 configure it too.
Acceptance on three ISAs unchanged; identities hot-plug.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

logs/20261014-134410/amd64/qemu-amd64-20261014-134410.log

@@ -0,0 +1,70 @@
+[=3hBdsDxe: loading Boot0002 "UEFI QEMU DVD-ROM QM00005 " from PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x2,0xFFFF,0x0)
+BdsDxe: starting Boot0002 "UEFI QEMU DVD-ROM QM00005 " from PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x2,0xFFFF,0x0)
+[=3hStarKernel UEFI Loader
+Loading kernel from ESP...
+[CKPT 001] Entered efi_main - ConOut live
+RAW SERIAL UP
+[CKPT 002] Serial (COM1) initialized
+Monolithic build - kernel linked directly
+Collecting boot information...
+CmdLine: parsed OK
+[CKPT 004] Command line parsed
+[CKPT 005] Kernel stack allocation decided
+[CKPT 006] Boot info collected (ACPI table located)
+GOP: linear framebuffer found
+[CKPT 007] GOP: linear framebuffer found
+[CKPT 008] About to enter ExitBootServices retry loop
+EBS...
+EBS OK
+Calling kernel_main (monolithic)...
+
+
+   _____ _             _  __                    _ 
+  / ____| |           | |/ /                   | |
+ | (___ | |_ __ _ _ __| ' / ___ _ __ _ __   ___| |
+  \___ \| __/ _` | '__|  < / _ \ '__| '_ \ / _ \ |
+  ____) | || (_| | |  | . \  __/ |  | | | |  __/ |
+ |_____/ \__\__,_|_|  |_|\_\___|_|  |_| |_|\___|_|
+
+LithosAnanke v2.1.0 amd64
+Architecture: amd64
+Build: Oct 14 2026 13:43:44
+
+UEFI BootServices: EXITED
+Console: serial line is a 16550 at port 0x00000000000003f8 (COM1, probed)
+
+=== StarKernel Boot Information ===
+Memory map entries: 131
+Total memory: 1023 MB
+Usable memory: 968 MB
+===================================
+
+PMM initialized.
+PMM statistics:
+  Total pages: 249318
+  Free pages : 247795
+  Used pages : 1523
+  Total MB   : 973
+  Free  MB   : 967
+  Used  MB   : 5
+
+VMM initialized (mapped RAM, CR3 switched)
+VMM initialized (mapped RAM, CR3 switched)
+VMM self-test: mapped OK at 0xffff800000000000
+VMM self-test complete.
+
+IDT installed.
+
+APIC: init...
+APIC: IA32_APIC_BASE MSR=0x00000000fee00900
+APIC: stale-ISR drain: 0 EOI(s) issued
+APIC: initialized (xAPIC MMIO, TPR=0, SIVR=0x1FF, EOI-clear)
+APIC: init done
+
+I/O APIC: init...
+I/O APIC: base=0xfec00000, gsi_base=0, overrides=5
+  override: source=00 gsi=2 flags=0x0000
+  override: source=05 gsi=5 flags=0x000d
+  override: source=09 gsi=9 flags=0x000d
+  override: source=0a gsi=10 flags=0x000d
+  override: source=0b gsi=11 flags=0x000d